Process of coating bodies with tungsten



J. A. M. VAN HEMP? LWEQM PROCESS OF COATING BODIES WIflH TUNGSTEN Filed Dec. 2, 1924 Patented July 29, 1930 UNITED STATES PATENT OFFICE J'OHANNES ANTONIUS MARIA VAN LIEMPT, 0F EINDIIOVIEN, NETHERLANDS, ASSIGNOR TO N. V. PHILIPS GLOEILAMPENFABRIEKEN, OF EINDHOVEN, NETHERLANDS PROCESS OF COATING BODIES WITH TUNGSTEN Application filed December 2, 1924, Serial No.

The invention comprises a process of coating bodies with tungsten.

According to the invention the process of coating with tungsten a body consisting of electrically conducting material consists in that a fused tungstate or amixtureof fused tungstates is electrolyzed at such a current density that tungsten is isolated as a coherent layer on the body which isconnected as a cathode. Tungstates are compounds of the composition nX OmWO if n and m are whole numbers and X is a metal. It has been found that the electrolysis according to the invention can be carried out with very favourable results, if the current densityislower than 100 milliamp. per cm of the surface of the cathode. As a rule it is advisable to start from a tungstate or a mixture of tungstates having a low melting oint. According to the invention, prefera ly a fused alkali tungstate or a mixture of fused alkali tungstates is electrolyzed. Particularly favourable results are obtained in the electrolysis of lithium tungstate (Li WO4), but also with other alkali tungstates the electrolysis can be carried out with favourable results.

According to the invention the temperature at which the electrolysis is carried out is preferably over 900 Centigrade, as it may occur that below 900 centigrade tungsten nebulae are produced, which do not separate on the cathodes as a solid but remain colloidally dissolved in fusion. It is generally preferable that the temperature at which the electrolysis is carried out should not be-too close to the melting point of the tungstate or the mixture of tungstates, because if this temperature dif-' ference is too small this would involve a high degree of viscosity of the molten mass, which is injurious to-the electrolytic-process. The condition herein set up is satisfied, for examle, by lithium tungstate (LEW-O which melts at about 7 50 centigrade but also an eutectic mixture of lithium tungstate (LlgWOg) and potassium tungstate (K WO having a melting point of say 500- centigrade or a sodium (Na WO and potassium tungstate (KQWOQ that melts at about 650 centigrade may be used with advantage but also with other tungstates of the 753,452, and in the Netherlands June 28, 1924.

composition nX OmWO favourable results These tungsten bronzes are sometimes produced even if the excess of N0 is but 5%.

According to the invention the body onwhich tungsten is precipitated may consist of a single tungsten crystal. The body has been found to increase in this case whilst keeping its one-crystal structure so that an one-crystal body can thus be produced" which is larger than the original one. For this purpose onecrystal wires, rods or the likeof tungsten are,

during the electrolytic treatment preferably connected as a cathode in front of an anode which surrounds the cathode substantially.

Such an anode, may, for example, be cylindrical or it may consist of little rods that are arranged parallel to each other in the shape,

of a many sided prism.

The invention will be more clearly understood by reference to the accompanying drawmg. lithium tungstate (Li VVO are arranged two electrodes 2 and 3, one of which, theanode, consists of tungsten whereas the other one, the cathode may be, for example, a body made of copper. The said electrodes are connected with the interposition of a potentiometer whilst 4 is a source of continuous current and 5 a regulating resistance. It is found that a regular isolation of tungsten occurs at the cathode and that the said tungsten rigidly adheres as a coherent layer to the cathode, if between the electrodes a tension of 0.08 volt is supplied and the current density is 7 5 milliamp. percm If the body that is wished to be sheathed with tungsten consisting of material to which tungsten adheres less readily it is preferable that the body should be first coated with a layer to which tungsten adheres readily.

In a porcelain crucible 1 containing peres per square centimeter.

Thus, for example, it is advisable that. a body of iron which is desired to be tungstened is first coppered andnot until then tungstened.

According to the invention bodies consisting of non conducting material may be tungstened by first coating them with one or more layers of electricity conducting material .before the coating with tungsten has been effected. Thus, for example, bodies-of nonconducting material may first be coated with graphite, then coppered a nd finally tungstened.

'When using a cylindrical anode a tungsten one-crystal wire connected'as a cathode, having a diameter of 300 microns and being plunged for three centimetres into fused lithium tungstate will within two hours increase in size to the extent of a tungsten onecrystal rod having a diameter of 2 milli- -metr es, if the tension at the, electrodes is 0.08

is 100 milliamvolt and the current density What I claim is:-

V 1. Aprocessof coatinga bodyyvith tungsten which comprises electrolyzing a fused alkaline tungstate at a current density which is lower than 100 milliamperes per square centimeter of the surface of the cathode, the body to be coated being connected as cathode.

2. A process of coating abody with tung: sten which comprises electrolyzing a fused alkaline tungstate at a current density which is lower than 100 milliamperes per square centimeter of the surface of the cathode, the body to be coated being connected as cathode and the temperature at which the electrolysis is carried out being over 900 centigrade.

In testimony whereof I afiix my signature, at the city of Eindhoven, this 25th day of October, 1924.

' JOHANNES'ANTONIUS MARIA VAN LIEMPT. 

